Editing TeX (section)

==History==

When the first paper volume of Knuth's ''[[The Art of Computer Programming]]'' was published in 1968,<ref>{{cite web|url=http://www-cs-faculty.stanford.edu/~uno/vita.html|title=Less brief biography|last1=Knuth|first1=Donald E|website=Don Knuth's Home Page|access-date=9 January 2017|archive-date=5 December 2016|archive-url=https://web.archive.org/web/20161205093445/http://www-cs-faculty.stanford.edu/~uno/vita.html|url-status=dead}}</ref> it was typeset using [[hot metal typesetting]] on a [[Monotype system|Monotype machine]]. This method, dating back to the 19th century, produced a "classic style" appreciated by Knuth.<ref name="Knuth Kyoto 1996">{{cite web|url=https://www.kyotoprize.org/wp/wp-content/uploads/2016/02/12kA_lct_EN.pdf|archive-url=https://web.archive.org/web/20180127194502/http://www.kyotoprize.org/wp/wp-content/uploads/2016/02/12kA_lct_EN.pdf|url-status=dead|archive-date=27 January 2018|title=Commemorative lecture of the Kyoto Prize, 1996|last1=Knuth |first1=Donald E|publisher=[[Kyoto Prize]]|access-date=18 August 2018}}</ref> When the second edition was published, in 1976, the whole book had to be typeset again because the Monotype technology had been largely replaced by [[phototypesetting]], and the original [[font]]s were no longer available. When Knuth received the [[galley proof]]s of the new book on 30 March 1977, he found them inferior. Disappointed, Knuth set out to design his own typesetting system.

Knuth saw for the first time the output of a high-quality digital typesetting system, and became interested in digital typography. On 13 May 1977, he wrote a memo to himself describing the basic features of TeX.<ref>{{Citation | first = Donald Ervin | last = Knuth | url = https://www.saildart.org/TEXDR.AFT&#91;1,DEK&#93;1 | archive-url = https://web.archive.org/web/20150112075949/https://www.saildart.org/TEXDR.AFT%5B1%2CDEK%5D1#91;1,DEK&#93;1 | url-status = dead | archive-date = 2015-01-12 | title = TEXDR.AFT }}</ref> He planned to finish it on his [[sabbatical]] in 1978, but as it happened, the language was not "[[Freeze (software engineering)|frozen]]" (ready to use) until 1989, more than ten years later. [[Guy L. Steele, Jr.|Guy Steele]] happened to be at [[Stanford University|Stanford]] during the summer of 1978, when Knuth was developing his first version of TeX. When Steele returned to the [[Massachusetts Institute of Technology]] that autumn, he rewrote TeX's input/output ([[I/O]]) to run under the [[Incompatible Timesharing System]] (ITS) operating system. The first version of TeX, called TeX78, was written in the [[SAIL programming language]] to run on a [[PDP-10]] under Stanford's [[WAITS]] operating system.<ref>{{FOLDOC|TeX}}</ref>

=== WEB and literate programming ===
For later versions of TeX, Knuth invented the concept of [[literate programming]], a way of producing compilable [[source code]] and cross-linked documentation typeset in TeX from the same original file. The language used is called [[WEB]] and produces programs in DEC PDP-10 [[Pascal programming language|Pascal]].

=== TeX82 ===
TeX82, a new version of TeX rewritten from scratch, was published in 1982. Among other changes, the original [[hyphenation algorithm]] was replaced by a new algorithm written by [[Frank Liang]]. TeX82 also uses [[fixed-point arithmetic]] instead of [[floating-point arithmetic|floating-point]], to ensure reproducibility of the results across different computer hardware,{{sfn|Knuth|Plass|1981|p=144}} and includes a real, [[Turing completeness|Turing-complete]] programming language, following intense lobbying by Guy Steele.<ref>Knuth, Donald E. ''[http://maps.aanhet.net/maps/pdf/16_15.pdf Knuth meets NTG members]'', NTG: MAPS. '''16''' (1996), 38–49. Reprinted as ''Questions and Answers, III'', chapter 33 of ''Digital Typography'', p. 648.</ref> In 1989, Donald Knuth released new versions of TeX and [[Metafont]].<ref>Knuth, Donald E. [http://www.tug.org/TUGboat/Articles/tb10-3/tb25knut.pdf ''The New Versions of TeX and METAFONT''], TUGboat '''10''' (1989), 325–328; '''11''' (1990), 12. Reprinted as chapter 29 of ''Digital Typography''.</ref> Despite his desire to keep the program stable, Knuth realized that 128&nbsp;different characters for the text input were not enough to accommodate foreign languages; the main change in version 3.0 of TeX is thus the ability to work with [[8-bit]] inputs, allowing 256 different characters in the text input. TeX3.0 was released on March 15, 1990.<ref>{{Cite book |last=Hoenig |first=Alan |url=https://books.google.com/books?id=-xzeQtE4y0kC&dq=TeX82+published+in+1982&pg=PA8 |title=TeX Unbound: LaTeX & TeX Strategies for Fonts, Graphics, & More |date=1998 |publisher=Oxford University Press |isbn=978-0-19-509686-6 |language=en}}</ref>

Since version 3, TeX has used an idiosyncratic [[software versioning|version numbering system]], where updates have been indicated by adding an extra digit at the end of the decimal, so that the version number [[asymptotically]] approaches [[Pi|{{pi}}]]. This is a reflection of the fact that TeX is now very stable, and only minor updates are anticipated. The current version of TeX is 3.141592653; it was last updated in 2021.<ref>{{cite web|title=TeX 21 release|url=http://ftp.cs.stanford.edu/pub/tex/tex21.tar.gz|access-date=2022-01-05}}</ref> The design was frozen after version 3.0, and no new feature or fundamental change will be added, so all newer versions will contain only [[Software bug|bug]] fixes.<ref name=":1">{{Cite web|url=https://texfaq.org/FAQ-TeXfuture|title=What is the future of TeX?|date=2018-05-27|website=The TeX FAQ|access-date=2019-07-21|archive-date=28 April 2019|archive-url=https://web.archive.org/web/20190428184722/https://texfaq.org/FAQ-TeXfuture|url-status=dead}}</ref> Even though Donald Knuth himself has suggested a few areas in which TeX could have been improved, he indicated that he firmly believes that having an unchanged system that will produce the same output now and in the future is more important than introducing new features. For this reason, he has stated that the "absolutely final change (to be made after my death)" will be to change the version number to {{pi}}, at which point all remaining bugs will become features.<ref>Knuth, Donald E. [http://www.ntg.nl/maps/05/34.pdf ''The future of TeX and METAFONT''], NTG journal MAPS (1990), 489. Reprinted as chapter 30 of ''Digital Typography'', p. 571.</ref> Likewise, versions of Metafont after 2.0 asymptotically approach {{Mvar|[[E (mathematical constant)|e]]}} (currently at 2.7182818), and a similar change will be applied after Knuth's death.<ref name=":1" />

=== Public domain ===
Since the source code of TeX is essentially in the [[public domain]] (see below), other programmers are allowed (and explicitly encouraged) to improve the system, but are required to use another name to distribute the modified TeX, meaning that the [[source code]] can still evolve. For example, the [[Omega (TeX)|Omega]] project was developed after 1991, primarily to enhance TeX's multilingual typesetting abilities.<ref>{{Cite web|url=https://texfaq.org/FAQ-enginedev|title=TeX Engine development|date=2018-05-24|website=The TeX FAQ|access-date=2019-07-21|archive-date=28 April 2019|archive-url=https://web.archive.org/web/20190428184859/https://texfaq.org/FAQ-enginedev|url-status=dead}}</ref> Knuth created "unofficial" modified versions, such as [[TeX-XeT]], which allows a user to mix texts written in [[Bi-directional text|left-to-right and right-to-left]] [[writing system]]s in the same document.<ref name="autogenerated1"/>